1. Field of the Invention
Embodiments in accordance with the present disclosure are directed to integrated circuits containing voltage regulators.
2. Description of the Related Art
A voltage regulator is an electronic circuit that provides a regulated voltage to a load. One problem with voltage regulators is that if the load changes, the voltage regulator may have difficulty maintaining the voltage at a target level. For purposes of illustration, the following example is provided of the difficulties that can occur when using a voltage regulator to supply voltages to a memory array of non-volatile storage elements. In the following example, the non-volatile storage elements are of a variety that store information based on a detectable change in state (state change elements).
Materials having a detectable level of change in state, such as a resistance or phase change, are used to form various types of non-volatile semiconductor based memory devices. For example, some materials (e.g., carbon) can be switched between low and high resistance states. These types of materials can be used to form re-writable memory elements. Multiple levels of detectable resistance in materials can further be used to form multi-state devices which may or may not be re-writable.
In many implementations, a memory array is arranged as a set of word lines and bit lines that are substantially perpendicular to each other with a memory element at the intersection of each word line and bit line. Thus, two-terminal memory elements can be constructed at the intersections with one terminal (e.g., terminal portion of the cell or separate layer of the cell) in contact with the conductor forming the respective word line and another terminal in contact with the conductor forming the respective bit line.
Programming and reading of the memory elements typically involves applying certain voltages to the word lines and bit lines. For example, a relatively large program voltage may be applied across a memory element by applying appropriate voltages at a certain word line and bit line.
Reading the memory elements typically involves applying a read voltage that is smaller than the program voltage. The program state of the memory element can be sensed by the amount of current that flows through the memory element in response to the read voltage. In some implementations, the memory element current causes a drop in voltage at a reference node based on the capacitance of the reference node. After a period of time, the voltage at the reference node is compared with a reference voltage to determine the program state of the memory element.
A power management circuit in a memory array has a linear voltage regulator that provides the voltages to read (and program) the memory elements. However, under some circumstances the load current on the voltage regulator changes very rapidly. The change in load current causes a ripple of the output voltage of the voltage regulator. Unfortunately, this voltage ripple interferes with the ability to accurately sense the state of the memory element. In some implementations, the voltage ripple causes a capacitive current due to one or capacitances in the memory sense circuit. Note that this capacitance may be a parasitic capacitance and is not the aforementioned capacitance of the reference node. However, this capacitive current may lead to an error when comparing a reference current with the memory element current. That is, the capacitive current can add to or subtract from the memory element current, which alters the rate at which the voltage at the reference node changes.
In one implementation, the problem is overcome by delaying the sensing of the memory element until the voltage ripple settles down. However, this adds to the time needed to sense the state of the memory elements.
Another possible solution is to add an amplifier to the circuit to provide a large pre-charging current prior to sensing the state of the memory element. The pre-charging current may prevent the voltage ripple from occurring, or at least substantially reduce the voltage ripple. However, the amplifier that is needed to adequately reduce the voltage ripple needs to be a fast amplifier that consumes considerable power to eliminate the voltage ripple.